Balancing of automobile wheels, truck wheels and the like is normally carried out in a commercial garage by more or less permanent equipment at the garage. Static type balancers as opposed to dynamic balancers are normally used. Essentially, the wheel is balanced by positioning the hub opening over a conical structure which centers the wheel, the conical structure itself being supported at a single fulcrum point slightly above the center of gravity of the wheel. Any tilting of the wheel will indicate an imbalance.
Other types of static balancing devices operate on the principle of suspension balancing wherein a hollow vertical shaft includes a suspending wire secured within the shaft at an axial point and passing out the top of the shaft. A wheel supporting plate structure in turn is centrally secured to the shaft in a horizontal plane and the hub opening in the wheel to be balanced rests on this plate with the hollow shaft passing through the center of the opening.
If the wheel is precisely coaxially centered with respect to the shaft and suspending wire, any imbalance will result in tilting and can be immediately observed by the position of the suspending wire passing out the top of the shaft; that is, it will be closer to one peripheral portion than another.
In order to provide precise coaxial centering of the wheel hub opening relative to the shaft and suspending wire, a conical arrangement could be provided on the supporting plate similar to those used in commercial garages. However, variation in the size of the wheel hub opening and different distances of the plane of the opening from the center of gravity of the wheel result in different levels of the wheel being supported by the conical portion and thus a shift in the center of gravity of the wheel relative to the fixed point within the vertical hollow shaft at which the suspending wire is connected. The sensitivity of the balancing system is thus dependent upon the size of the hub opening and the geometry of the wheel.
In an effort to overcome the foregoing problems, various arrangements for supporting the hub opening of a wheel in an exact coaxial relationship on a flat plate have been proposed. For example, three radial projections from the surface of the plate could engage interior circumferentially spaced points of the hub opening to hold the wheel on the plate in coaxial relationship. However, the exact positioning of these projections at precisely equally radially spaced points from the shaft axis would have to be tailored for each different sized hub opening. It is vitally important that the wheel hub opening be precisely coaxially centered with respect to the suspending wire and shaft if accurate balancing is to be achieved.